So when I add a private category for a group, I can only manage the first type of group but not the latter that interests me the most.

For example, I wish I could have a private category for Ambassadors. As we have a group of over 100 volunteers and I'll have to add them manually already once to the second type of group, I wish I didn't have to repeat that process to add them to the private category.

Is there a way to avoid that process?

Also why are the two groups name similarly when they are two different things?